Two types of pen tips adapted for writing tools for writing fine letters or drawing fine lines are known in the art. One is a synthetic resin pen tip having an ink flowing channel of a suitable shape bored through a plastic casing in its axial direction. This type of pen tip is generally used for writing fine letters. The other type is a tubular writing pen tip wherein a weight is attached to the rear end of a core member which is loosely fitted through a fine tubular member. The front end of the core member slightly projects from the writing face so that it can be retracted by the writing pressure. This type of pen tip is generally used for mechanical drawing or drawing fine lines.
The synthetic resin pen tip can be easily produced since the ink flowing channel is formed at the same time as thermoplastic material is shaped into a tubular member by injection molding or extrusion molding. However, such a pen tip can only be made of easily formable materials. Another defect is that a letter or line of a constant width cannot be consistently written. Furthermore, the properties of materials other than thermoplastics which have good adaptability to writing fine letters or lines cannot be effectively utilized. Hence, it has been difficult to produce a hard and rigid wear resistant pen tip or a resilient durable pen tip.
The tubular writing pen tip of the second type can be produced from a hard and rigid material (e.g. metallic material) or combinations of two or more materials, but then, such a pen tip does not meet all requirements for writing fine letters. An acceptable writing pen for fine letters must not only write smoothly at various writing angles but it must also generate a sufficient amount of ink flow out to provide fine letters consistently. The tubular writing pen tip satisfies these requirements when it is used at an angle almost normal to the paper on which the letters are written, but not at other writing angles. A pen tip that satisfies these requirements for various writing angles has not yet to be developed, and accordingly a requirement for an improved pen tip remains for consideration.
German patent application (OLS) No. 3,023,189 discloses a tubular writing pen tip wherein the weight attached to the rear end of the core member is replaced by a sponge or other porous elastic material in contact with the rear end of the core member. The core is allowed to protrude out of the small tube by impact resilience of the sponge. This tip reduces undesirable scratching of the projection of the core member on the writing surface and enables writing with an upwardly facing pen tip. Despite these advantages, the requirements for acceptable consistent writing of fine letters are not met by this pin tip. During writing, the core member vibrates so much that consistent good writing is not achieved. Moreover, the ink flow varies slightly between compression of the porous elastic material and release of the compression, as well as varying between two writing angles. As a result, consistent production of sharp fine letters is not easily accomplished. Additionally, the impact resilience of the porous elastic material is unavoidably decreased with time or because of repeated stresses, and therefore the initial performance of the pen tip cannot be retained.
The core member of the pen tip of German patent application (OLS) No. 3,023,189 functions as an ink guide and provides cleansing effect, but it is not a substantial part of the writing tip during writing, and instead, the front annular end of the tube itself forms a substantial writing tip. This is another reason why good ink flow and smooth writing are not achieved at an angle other than normal to the surface of the paper on which letters are written.